Modular building construction has the advantages over conventional construction in the field of lowered construction costs, shortened construction schedules, and a controlled building environment that reduces waste. By using automatic assembly equipment and repetitive assembly-line techniques, factories can assemble modules for buildings more efficiently and with greater consistency in product quality than buildings built conventionally in the field. A trained and closely supervised factory workforce, with lower labor rates than those found of workers in the field, assembly line efficiencies with precision jigs, and construction in a controlled environment with material protected from the elements all add to the cost saving benefits of modular construction.
Historically, there are two challenges in the modular building construction industry. The first is to complete as much of the modules as possible in the factory because once onsite, labor, materials, and coordination are much more expensive and harder to control. The second is delivery itself; the expense of moving large modules long distances continually threatens the industry's ability to be cost competitive.
To maximize the work completed in the factory and to maximize assembly line efficiencies, it is standard practice in the modular building industry to use module sizes that conform to the maximum width, length, and height allowed on the roadways over which the modules will travel. Typical modules are 12′-0″-16′-0″ wide, 14′6″ tall, and anywhere from 30′-60′ long.
While this practice reduces the total number of modules needed to create the building, over-dimensioned modules must be transported on specialized trucks and specialized routes with large enough roadways, greatly impacting the costs associated with delivery of the modules to the field.
Due to the cost of shipping on these specialized trucks and routes, there are regional limitations in this industry that are tied to the geographic location of the respective factory. A factory will typically only service within a 200 mile radius of its location, as transporting the modules from the factory to a site beyond this range quickly becomes cost prohibitive. These regional limitations greatly impact the markets that can be served by a factory in the modular building industry.
Though the work needed to be performed in the field after the modules have been delivered is typically focused in the areas where modules are adjoined, this scope of work can vary greatly depending on how much preplanning went into the sizing of the structure of the modules and the subsequent thickness of the finishes and cladding to be installed, the precautions the factory takes to protect finishes, windows and doors, and other external features, as well as the complexity of the arrangement of the modules once adjoined and positioned on site.
In an effort to minimize the delivery costs, the modules are typically afforded minimum protection from potential damages that may arise from transporting the modules on roadways. It is standard practice in the industry to use plastic sheeting, or “shrink wrap”, to protect the sides of the modules. Though this offers adequate protection for rough sheathings and rough assemblies, it does not offer enough protection for finish materials and finish assemblies. As a result, the factory will typically not install exterior finishes or exterior windows and doors for fear of potential damage during transport.
In addition, due to the limitations placed on the maximum width of the module by roadway requirements, every additional inch of thickness to the width of the module can have huge consequences on the routes allowed and the associated costs of delivery. Because factories prefer to build all modules with the same width for ease of assembly and fabrication within their jigs and not all of the modules used to create a building require exterior cladding and the addition of exterior cladding adds to the overall width of modules, it is standard practice to not deliver modules with exterior cladding and exterior windows and doors, thereby maximizing the width of all the modules for transport. In addition, since access is usually required in the field where modules are joined together, the exterior cladding and interior finishes typically cannot be installed on the modules in the factory at the locations that modules are to be joined. Since factories prefer to complete all of the exterior cladding and interior finishes at the same time, again it is standard practice to leave off the exterior cladding and much of the interior finishes and to complete the entirety of this work in the field.
It is also standard practice in the industry to not install the roofing in the factory as the slope of the roof adds additional height to the module that may cause the module to be over the maximum height restrictions of the roadways while it is on the truck.
Only completing modules to a semi-finished state is another key limitation in the modular industry. Typically 40-50% of modular building construction is left to be completed in the field after the modules have been delivered, subjecting that work to unpredictable labor costs in the field and unpredictable weather in the field, dramatically affecting the overall building construction cost. This work is typically not completed by factory labor, but is handed off to a local general contractor and a multiplicity of trades people to complete the building, all whom have limited product experience and limited knowledge of the work done to the modules in the factory and the work needed to be completed in the field to finish the modules. This often unclear division of labor leads to finger pointing about who should take responsibility for what work and also has implications on warranty coverage.
In an attempt to confront the regional limitations of the modular industry due to its construction and delivery methods, there are two new practices in the modular building industry to utilize modified shipping containers or container-like structures as the modules to construct a building in an attempt to be able to deliver them utilizing the intermodal transportation network. In contrast to the specialized trucks required to transport typical building modules, the shipping container industry utilizes shipping containers that are transported via a global infrastructure network of trucks, rails, and ships established to move shipping containers practically anywhere in the world at low cost and with ease. Due to their size, the modules typically used in the modular-building industry cannot be transported on this network.
The first new practice, the use of modified shipping containers, is fundamentally problematic for utilization in building construction and habitation. Shipping containers are un-insulated and due to the lack of framed construction and the use of metal skins for the roof and walls, it is difficult to add plumbing, mechanical, and electrical systems. Given the dimensional limits of the containers, typically 8 feet wide and 9-6 feet tall, the need to add insulation and framing at the walls, insulation and roofing membrane at the roof, ceiling framing and finish flooring over the plywood subfloor of the container, all of which can only be added inside the metal skins of the container, causes the spaces within the container to not be comfortably habitable in regards to room widths and ceiling heights.
Additionally, because the metal skins forming the exterior walls are integral to the structural integrity of the shipping container, when they are cut to allow for openings they severely compromise the structural integrity of the container and additional structural support must be added. Once the shipping container has been modified, though it typically no longer meets all of the standards for the transport of cargo for a shipping container for intermodal transport, it still can be shipped utilizing the intermodal transportation network. However, depending on the amount of modifications made to the container, it typically can no longer structurally perform to or otherwise meet the standards required for a shipping container and thus might have to be transported in a similar manner as the standard building modules, via a specialized truck or flatbed. Additionally, after modifications and openings in the external metal skins have been made for habitation, the shipping container is no longer protected at those openings during transport.
Further, in the shipping industry's effort to maximize the interior storage volume of the container, the external metal skin of the container is set back from the outside faces of the corner fittings the absolute minimum amount to allow the fittings to be engaged with the standard load handling equipment used in the intermodal network. The dimensional relationship between the metal skin and the corner fittings precludes the ability to add any exterior cladding, windows or doors, and roofing to the container that would protrude beyond the metal skin and still have the container be able to be handled properly via the intermodal network. This translates to exterior cladding, windows, doors and roofing not being able to be installed in the factory and subsequently needing to be installed in the field after the containers have been transported from the factory.
A second new practice in the modular building industry is to utilize container-like structures, that are essentially structures built to the specifications of a shipping container, rather than modifying existing shipping containers. These container-like structures have the ability to be transported via the intermodal network. Because these container-like structures do not solely rely on the metal skin for their structural integrity, they offer the advantage of more flexibility to have larger openings than by modifying and cutting an existing shipping container. However, in their attempt to conform to the intermodal requirements of a shipping container and their acceptance of only attaining a semi-finished state of completion to the container-like structures in the factory prior to transport, they typically rely on a metal skin to form their walls and roofs much like shipping containers. These container-like structures thus have the same dimensional restrictions between the external metal skin and the corner fittings that preclude the ability to add any exterior cladding, windows or doors, and roofing to the container-like structure while still being able to be handled properly via the intermodal network. Accordingly, most of the work to create a habitable building must be completed in the field.
In U.S. Pat. No. 4,854,094 a method is disclosed for creating a habitable building utilizing standard shipping containers that are transported to the field. The shipping containers are not fit for habitation. After they have been joined in the field, various materials are added to the shell of the containers to complete the building and make it habitable. This work includes opening portions of adjoining walls between the containers to create a larger habitable space, installing a raised floor, installing a roof over the containers, installing a dropped ceiling and insulation, installing interior wall finishes and insulation, installing a weather resistant exterior cladding and exterior insulation, opening up walls for windows and doors and installing windows and doors. While the shipping containers can be transported to the field via the intermodal network, it is clear that the benefits of modular building whereby modules can be constructed in a controlled factory environment are not afforded to a system where the majority of the work is necessitated to be completed in the field.
In U.S. Pat. No. 5,706,614 a method is disclosed for creating a habitable building utilizing shipping containers, whereby the shipping containers are modified in a factory environment before being transported to the field. The modifications to the shipping containers include securing a weather resistant outside covering to the outside of the corrugated metal skin of the containers, securing a plastic roof cap to the top of the container roof, providing windows and doors in the openings cut in the walls of the container, securing inner walls and insulation, securing a ceiling structure and insulation and providing a finish flooring. While completing this work before the containers are transported to the field affords this system the benefits of construction in a controlled factory environment, the modifications made to the shipping containers preclude them from being able to be transported via the intermodal network. The additional exterior roof, additional exterior wall covering and additional windows and doors that are added to make the container fit for habitation all protrude beyond the metal skin and the corner fittings of the container, making the container no longer able to be handled properly via the intermodal network.
In U.S. Pat. No. 4,891,919 a method is disclosed for constructing a containerized home, which in its unassembled state has the size and shape of a standard “high cube” steel shipping container, whereby in the field the steel walls of the container-like structure will unfold and composite panels stored within the container-like structure are then attached to form the outer walls of the home. While the transportable container-like structure has the same size and shape of a standard cargo shipping container and can be transported to the field via the intermodal network, all of the exterior walls, windows and doors, interior walls and roofs that are needed to make the container-like structure fit for habitation, are stored within the container-like structure and are then assembled in the field to complete the building and make it habitable. While the container-like structure can be transported to the field via the intermodal network, it is clear that the benefits of modular building whereby modules can be constructed in a controlled factory environment are not afforded to a system where the majority of the work is necessitated to be completed in the field.
In all of the above cases, even though a shipping container or a container-like structure is being used as the basis for a building module, these designs either structurally undermine the module so that they cannot ship safely or efficiently through the intermodal network or they arrive in a semi-finished state and require extensive, expensive, and unpredictable site-work to make the buildings fit for habitation.